Normally a device of this type consists of a matrix of image points called pixels, rectangular in shape, and the integrated circuit of the sensor is also rectangular. However, for numerous endoscopic applications and other applications requiring a very small size sensor, this rectangular shape is not ideal because the rectangular shape fills only a portion of the circular surface that usually corresponds to the space available for the device. The field of vision covered by a lens, which is typically circular, does not correspond to the sensitive surface of the rectangular sensor and either it covers only a portion of the lens's field of vision, or a sensor is used with corners that extend beyond the field of vision covered by a circular lens.
Since the rectangular shape of the assembly of a set of photosensitive cells for capturing an image is often poorly adapted to space constraints, numerous solutions have been proposed to achieve better adapted detectors. For example, U.S. Pat. No. 7,009,645 proposes an image sensor with a circular arrangement of photosensitive cells. The photosensitive cells are addressed for sequential reading according to a polar coordinate addressing system along beams and in circles. This arrangement has two major flaws, as a result of which such an arrangement is seldom used. First, the spatial resolution of such an arrangement of photodetector cells is not uniform and increases towards the center, and although measures for reducing the impact of this have been proposed, no perfectly uniform resolution has been obtained. Second, the majority of algorithms for treating images and displaying images are based on the image points being arranged in lines and columns, therefore it is imperative for such a sensor to convert to this image presentation format, requiring very burdensome calculations in order to transform space coordinates.
One known image sensor comprises a matrix of photosensitive elements whose individual signals are queued in a sequential process by addressing lines and columns of said photosensitive elements. This sequential addressing is achieved using a line addressing circuit placed along a peripheral edge of the matrix and a column addressing circuit which is along the other peripheral edge of the matrix.
Such a device works well when the sensor is square or rectangular in shape so that the addressing of lines and columns defines the image points without any overlap. For polygonal shapes, for example, simple addressing where each image point has a unique line address and a unique column address is not possible with only one of the elements, either line addressing or column addressing, placed along a peripheral edge of the device when the polygon does not contain at least a minimum of one rectangular angle, because in that case, at least along one side of the polygon, the line decoder and the column decoder must be placed at the same time.
Solutions using arrangements of photoelectric cell matrices with one or two corners cut off, for example as shown in U.S. Pat. No. 5,291,010 have been proposed, but the line addressing circuits and the column addressing circuits remain respectively on individual sides of the polygon.
Particularly in the field of CCD type detectors for intra-oral X-ray radiation detection applications, there have been solutions proposed for this problem that may consist of establishing arrangements of photosensitive cell matrices organized along lines and columns, but with all four corers cut (essentially octagonal in shape) have been proposed. Some of these solutions only work with CCD type detector devices (charge-coupled Devices) where the period of the detector matrix is essentially larger than the minimum space necessary for placement of the addressing electronics, as is often true in intra-oral X-ray applications. In CCD technology there is no need for addressing along lines strictly speaking. Instead of a system of addressing along columns, the signal exiting a column is rather transferred along a readout register called “horizontal,” from one column to the other. Thus, European Publication EP 1255401 proposes a solution for addressing a CCD type matrix designed for intra-oral applications with cut corners where line addressing passes through the horizontal readout register in an upper conductive layer. Such an embodiment remains limited to CCD type detectors and cannot be generalized to sensor matrices where each pixel must, for reading, be directly connected to a readout circuit, as is the case, for example, with detector matrices made using CMOS technology (Complementary Metal Oxide Semiconductor) allowing the realization of very small detector cells, of the order of some micrometers or even less than one micrometer, for the smaller pixels currently in use.
US Publication 2006027625 proposes another solution that can only be achieved through CCD technology for realizing an orthogonal matrix with obliquely cut corners, but which requires a readout register along the lines that can transfer the charges received from the obliquely cut columns to each time pulse of said column registers. This property is only available for CCD type detectors.
US Publication 20090033777 proposes a solution for a matrix of photosensitive cells addressed in lines and columns that may be achieved using CMOS technology, but it is limited to situations where the oblique sides are generally smaller than the orthogonal sides because the addressing blocks for either the lines or the columns on the oblique sides are placed behind the respective block on the orthogonal sides and are interconnected by a network of connections on the oblique sides. This network of interconnections in the context of a highly miniaturized application such as endoscopy, for example, may lead to an unwanted increase in the total surface.
Japanese Publication JP210273757 proposes an embodiment of the device comprising a matrix of generally circular shaped photodetector cells. However, it proposes maintaining the matrix of photoelectric cells in a rectangular or square shape, but using the space available along the centers of the orthogonal edges of the matrix for placement other electronic components necessary for the operation of a radiation detection system, specifically for capturing a highly integrated image. In another variation of this proposal, it is suggested to resolve the problem of addressing and readout in the matrix by placing a second electronic readout element in a second integrated circuit plane and interconnect the matrix of photodetector cells using 3D integration with the readout circuit. This considerably raises per unit production costs. The process of placing such a device on a production plate is limited to hexagonal shapes and if the plate is cut using a rectilinear sawing process, it generates a greater than 50% loss of potential surface on a production plate, such that the production cost for such a device is vastly increased. An alternative sawing process might consist of circular cutting, which is not a standard procedure for wide scale production of electronics.
French Publication No. 2 930 841 describes a device comprising a set of electromagnetic radiation-sensitive detectors for endoscopic applications with a configuration similar to the device described. However, the arrangement and the geometry of the addressing circuits differ and it does not offer the same advantages. More specifically, the device described in this publication requires an increased number of transistors to be integrated within each pixel, which is undesirable in the context of an endoscopic application where the size of each pixel is advantageously kept as small as possible in order to increase resolution in a detector with a reduced surface.